This year on my 'Balcony of plenty' I grew:
Santa mini plum tomatoes as cordons. I used the deep planting in half a growbag method and I am still picking ripe toms.
I grew climbing beans up a wigwam of 6 foot canes, and got 2 lots of beans off one pot.
Also grew Californian Wonder peppers and Redskin. Redskin did particularly well. Cayenne peppers too, although yet to test their heat.
Also considered lettuce (mizuna or rocket type?) carrots, spring onions, and radishes.
I'll agree with strawbs, if your sister decides she likes them. I squashed 10 runners in to one growbag, and they seem to be doing well.
If you really want to splash out, how about one of the 'minarette' trees from Ken Muir?